This application proposes to continue current research on the timing of completion of childbearing and the length of the span of childbearing years, and is a resubmittal of an earlier application. The long-term objectives are to increase understanding of the age structuring of final childbearing among U.S. cohorts and subgroups, and of the ways in which these subgroups have differed in their timing of the first and subsequent births and in the number of children to result in the observed differentials in the timing of the final birth and the childbearing span. Another objective is to increase understanding of childbearing as an entire process, beginning with the first birth and proceedings with each successive birth, after varying intervals and with different probabilities of stopping childbearing. Specific aims include: (1) Complete the description of cohort and subgroup differences in the distributions of age at final birth and childbearing span, by describing how all three components of age at last birth (age at first birth, lengths of successive birth intervals, and completed family size or parity progression ratios) have simultaneously varied among cohorts and subgroups to produce the observed differences. (2) Decompose these cohort/subgroup differences in age at final birth and childbearing span to determine the relative contributions through their effects on its components. Methods to be used include existing techniques such as generalized linear models, as well as methods to be developed for the project. These include: methods for estimating birth intervals, parity progression ratios, and ages at first and last births from age-party-specific fertility rates; decomposing change in age at last birth to changes in the components; and decomposing the effects of covariates on age at last birth to the effects on the components. These methods proposed for development could have more general application.